It followed the rain criteria, but still contradicted the games. Rain induced by Rain Dance can't trigger the Sliggoo evolution in the games, but it did there. So the Goodra point counts.
So does the Johto example of Weepinbell, and please don't dismiss as early installment wierdness, because OS Johto wasn't as wierd as OS Kanto. In OS Kanto, I admit that many wierd things happened, and most events that happened there can be dismissed as early intallment wierdness. But OS Johto was far more closer to the overall norms of the anime.
Honestly, I'd rather have Steenee evolve here rather than not. Mallow's barely getting anything at all, getting shafted like anything, and finally she gets an episode focused on her. She at least should get something out of this episode, like an evolution.